This invention relates to a method and apparatus for testing the solderability of a component or for testing de-soldering wicks.
Wicks or braids for de-soldering are known for example from my U.S. Pat. Nos. 4,081,575 and 4,078,714, my U.S. patent application Ser. No. 849,616 and Hood U.S. Pat. No. 3,627,191. Such wicks absorb, by capillary action, the unwanted solder which is melted during repair or exchange of components on printed circuit boards or terminal, for example. Thus, the end of the wick and a heated soldering iron are pressed onto the deposit of solder which is to be removed, and as this solder melts the de-soldering wick absorbs it.
Such use of a wick reduces the thermal stress on the printed circuit board. Thus, the cold wick acts as a heat sink and reduces the rate of rise of temperature. The maximum temperature reached is limited because the de-soldering wick absorbs the solder as soon as it melts: the quicker a wick absorbs, the less the temperature will rise above the melting point of the solder, and the smaller the amount of heat energy which flows into the area. The total of heat energy applied depends upon the temperature level and the time for which an elevated temperature is present and both these factors influence the reliability of the materials and components in the de- soldering area. A quick-acting wick is desirable as it reduces both the temperature level and the time for which an elevated temperature is present.
However, the problem arises as to how a wick user may compare the different makes of wick available to him. There are no special test procedures available to test the absorption rates of the different wicks. A proposal which I have made in the past to users is to employ a comparison dip test based on Military Standard 202E (Apr. 16, 1973), method 208C. This Mil-Standard is a test for solderability of components (for example solid terminals or wires) and involves dipping the component briefly into a bath of molten solder, and observing the percentage area of the component which remains coated with solder after the component has been lifted from the bath. FIG. 208-1 of Mil-Standard 202E suggests a dipping device or apparatus for carrying out the test. This device comprises a beam pivoted at a point intermediate its ends and a rotary cam acting on one end of the beam to firstly lower and then raise the other end of the beam, from which is suspended the component to be subjected to the solderability test.
This Mil-Standard dipping device suffers the disadvantage that the dipping depth is not taken into account automatically. It is to be noted that, as the solder in the bath is used, the solder level lowers and the depth to which components are immersed is accordingly reduced. Also, timings are controlled by the rotary cam. Variations in the testing times are only possible by changing the motor speed or changing the cam. Motor speed control would introduce a further factor to be controlled and measured closely, in order to ensure that conditions are equal for all tests in a comparitive series.